Need Help Sizing an Engine.
 

Hey Guys,

I’m working on a project and need some help if you know how to size an engine for a plane. I recently bought the Laser Arrow Delta Wing and thought it would be fun to build an enlarged version as well. I had all the laser sheets duplicated at 150%. This model is going to be huge – at least for me. The original plane (wing) is 30" nose to tail, and 40 " wide, with a surface area of 780 sq in. The "Super Laser" will be 45" nose to tail, 60" wide and have 1,755 sq in. So I need some input on what size engine you think would lug this thing around. I was planning on putting a 75 size in the original one. I don’t have any other big planes or engines. I think I would like to stick to a two stroke, glow fuel type. I would really like a formula if there is one available to calculate a recommended engine size. Thanks for any input you may have.

Ken L.

Need Help Sizing an Engine.
 

Ken, you told us everything but the weight of the plane. To me, this is what I use. Lots of wing area is good, but I like to know how much the engine has to haul around. Let us know and we will try to help. By the way, how fast do you want it to fly??
Suptter

Need Help Sizing an Engine.
 

Any 46 will work!

Need Help Sizing an Engine.
 

Maybe two of them.... :stupid:

Request for more info.
 

Guys,

I don't have any idea yet how much it will weigh. Since I increased the size by 50% I assume the weight of the balsa and plywood would be 50 % greater. But since the surface area is 225% larger, I assume the weight of the Monokote will be quite a bit more. The box only has a weight of 1,500 g. I thought it was 2,200 g / lb. That would make the kit version less than a pound and that doesn't sound right to me. If you need to know the weight, I may just have to ask this question again when I'm finished building. OR - is there a rule of thumb for planes in weight ranges? Like 5-6 lbs .46, 7-8 lbs .60 etc? Maybe that can get me started.

As far as speed goes - I would like to hand launch it like the kit if possible. If I can't get enough speed off the line, I may have to add landing gear which I didn't particularly want to do. I'm not trying to go too big on the engine - just decent performance.

Thanks,
Ken

Need Help Sizing an Engine.
 

Hi!
I would go for a 10cc-15cc engine (.60-.90) as the span is 152cm and the lenght is about 115cm.
But it is also possible that it could fly well with a 7,5cc engine (.46). What it al boils down to is what performance you want.

Regards!
Jan K
Sweden

Engine Size
 

Ken, I think your on the right track with the weight and engine size like your last post. The added wing area will just give you lighter wing loading and should make for a better flying plane. I don't think the weight of the covering is going to make that much difference in the final weight of your plane, some...but not much. IMHO, there isn't anything wrong with using a bigger engine that you need, that's what the throttle's for, and it never hurts to have a little more power.
Suptter

Need Help Sizing an Engine.
 

Put the .75 in it....you'll be glad you did.... ;)

Need Help Sizing an Engine.
 

This sounds like it's going to end up between 7-9 lbs.

Stick a Jet 90L in the nose, and put landing gear on it. Your not going to try and hand launch a (Delta wing) plane of this size are you? I know I wouldn't.


Gary

No Hand Launch
 

Gary,

What's your opinion about not "Hand Launching" a plane like this. Would it be too big to get up to speed? Please elaborate.

Thanks,
Ken

Need Help Sizing an Engine.
 

Ken,

There are a lot of factors to consider when hand launching a plane....power to weight ratio being the most important. Overall weight is another. Also, what are you going to do, mount a launching handle on the bottom?

Will you always have a buddy there to help with the launch? By yourself? Ever try to hold out level in one hand a 60" plane? :eek:

I would take the time and put gear on it, even add retracts if it's the site of the gear hanging off the belly that you don't like.

To me, hand launching is more geared towards the lighter, .30 size and under planes.

I had the Balsa USA Enforcer (large Delta wing), and I can't imagine me trying to hand launch it. Sorry, I don't recall the wing span, but I think it was around 48"/49".

BTW, I had a ST .75 in it. (This was a "pusher") It could of used a Jet 90!! ;)

Gary